orthogonal dipoles fed with an opportune phase displacement,

placed close to the surface.

Our intention is showing that the considered AMC does not

enhance the CP properties of a radiating element different from

the spiral due to the particular properties of the radiated field. In

the first configuration, the dipoles are fed with a þ142 degrees

phase displacement. The chosen value is equal to the phase dis-

placement between the h and / electric field components of the

freestanding spiral. In this case, an elliptic polarization is radi-

ated by the dipoles. The intention is to underline that again no

improvement to the XPD is provided by the AMC. The case of

þ90 degrees phase displacement has been analyzed as well.

6. DIPOLES DESIGN

As the dipole is not a broadband antenna, we have designed it

to resonate in the first AMC band, i.e., around 2.2 GHz.

To make a comparison with the spiral, dipoles have been

placed at the same distance (k0/18) from the screen. Computa-

tions have been performed by using HFSS v.10.

In Figure 10, a plot of the XPD for the two analyzed config-

urations is given. In particular, we have compared the trend of

the XPD in freestanding case with the one in presence of the

AMC surface.

We can remark that the AMC does not provide any improve-

ment for the CP properties of the dipoles. In fact, in both cases

(þ90� and þ142� phase displacement), the XPD curve obtained

in presence of the artificial magnetic surface oscillates around

the maximum value reached in the freestanding configuration.

By using the spiral, on the contrary, two noticeable spikes of

XPD are visible at the AMC resonances in Figure 3. Moreover,

in the same figure, a slight decrease of the XPD is apparent

within the frequency regions far from the AMC resonances,

owing to the perfect electric conductor (PEC) behavior of the

screen, further proving that the circular polarization is given

exclusively by the presence of the AMC screen.

7. CONCLUSIONS

An artificial magnetic conductor has been proposed that is able

to efficiently convert an elliptic polarization into a circular one

if conveniently excited. Indeed, an increase of XPD can be

clearly observed at the AMC resonances (see Fig. 3). Moreover,

a slight decrease of the XPD is apparent in the frequency

regions far from the AMC resonance, owing to the PEC behav-

ior of the surface, further proving that the circular polarization

is given exclusively by the presence of the AMC screen.

ACKNOWLEDGMENTS

Elisa Carrubba wishes to thank Filippo Costa for his valuable

advices and useful discussions in carrying out this work.

REFERENCES

1. R.C. Johnson and H. Jasik, Antenna engineering handbook,

McGraw-Hill, New York, 1984.

2. J.M. Baracco, L.S. Drioli, and P.D. Maagt, AMC low profile wide-

band reference antenna for GPS and GALILEO systems, IEEE

Trans Antennas Propag 56 (2008), 2540–2547.

3. V.F. Fusco and S.W. Simms, Reflected circular polarization conser-

vation using textured surface, IEEE Electron Lett 43 (2007),

962–963.

4. D. Yan, C. Wang, C. Zhu, and N. Yuan, A novel polarization con-

vert surface based on artificial magnetic conductor, IEEE APM

Proceedings, 2005.

5. M. Diblanc et alter, Circularly polarized metallic EBG antennas,

IEEE MWCL 15 (2005), 638–640.

6. F. Yang and Y. Rahmat-Samii, A low profile single dipole antenna

radiating circular polarized waves, IEEE Trans Antennas Propag

53 (2005), 3083–3086.

VC 2010 Wiley Periodicals, Inc.

A COMPACT DVB-H ANTENNAWITH VARACTOR-TUNEDMATCHING CIRCUIT

Yue Li,1 Zhijun Zhang,1 Wenhua Chen,1 Zhenghe Feng,1

and Magdy F. Iskander21 State Key Laboratory of Microwave and Communications,Department of Electronic Engineering, Tsinghua University, Beijing,100084, China; Corresponding author: hardy_723@163.com2HCAC, University of Hawaii at Manoa, Honolulu, HI 96822

Received 19 October 2009

ABSTRACT: A reconfigurable varactor-based matching circuit isproposed in this article. The introduction of an extra series inductor into

the matching circuit reduces the required capacitance ratio of thevaractor from 27.9 to 8.2. A meander line DVB-H antenna is designedand fabricated to verify the concept. The dimensions of the prototype

antenna are 80 � 10 � 10 mm3, and it can provide better than �10 dBreturn loss across the 470–770 MHz bandwidth. VC 2010 Wiley

Periodicals, Inc. Microwave Opt Technol Lett 52: 1786–1789, 2010;

Published online in Wiley InterScience (www.interscience.wiley.com).

DOI 10.1002/mop.25317

Key words: reconfigurable antenna; varactor-tuned; compact

1. INTRODUCTION

Digital Video Broadcasting-Handheld (DVB-H) service can

deliver television programs or other multimedia content directly

Figure 10 Comparison between the XPD of the dipoles, fed with a

þ90� phase displacement (perfect CP) and with a þ142� phase displace-

ment (EP), in freestanding configuration and in presence of the AMC

screen. [Color figure can be viewed in the online issue, which is avail-

able at www.interscience.wiley.com]

1786 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 52, No. 8, August 2010 DOI 10.1002/mop

to mobile terminals. DVB-H operates at the frequency range of

470–770 MHz, which covers a relative bandwidth of 48.4%.

The typical dimensions of a handset are quite small in compari-

son to a quarter of wavelength at 470 MHz, so designing a pas-

sive internal DVB-H antenna to cover the whole band and pro-

vide good performance is always a challenge. One option is the

use of dual-resonant lumped elements to enhance bandwidth [1],

but this can only expand the bandwidth to a certain point.

Another attractive solution is the frequency reconfigurable

antenna [2, 3]. The working band of these antennas can be

dynamically switched or tuned. Although the antenna can only

cover a certain portion of the whole working band at any given

time, it is able to provide full coverage when all working states

are combined. In existing work, a variable capacitor (varactor)

is utilized to change the electric characteristic of antenna ele-

ment; RF switches and PIN diode are used to control the work-

ing length of the antenna to operate in different frequencies.

Several designs have been proposed for DVB-H antennas in

small devices [2, 3]. Compact in size, these designs can also

deliver the necessary impedance bandwidth and gain level. The

varactor in [2, 3] can continuously tune the antenna for a wider

frequency range and better performance. Both antennas proposed

in [2, 3] use a loading technique, loading the antenna by attach-

ing a shunt varactor between the end of the antenna and the sys-

tem ground. This limits options for the antenna element’s form

factor, since the antenna tail must be close to the system

ground.

This article proposes a new frequency-reconfigurable antenna

based on a tunable matching circuit. To verify the concept, a

meander line antenna element is designed to work with the

matching circuit. Better than �10 dB measured return loss

across the 470–770 MHz bandwidth has been achieved. The

dimensions of the meander line element are 80 � 10 � 10

mm3. The matching circuit includes an extra series inductor,

decreasing the required capacitance ratio of the varactor from

27.9 to 8.2.

2. MATCHING CIRCUIT DESIGN

To demonstrate the matching technique proposed in this article,

a meander line antenna is used as a design example. In fact, the

antenna element can be replaced by an antenna of any form fac-

tor, as long as it has similar frequency response. Figure 1 shows

the impedance curve of the original antenna on a Smith Chart.

Specific antenna dimensions can be found in Figure 2. Three

markers on the curve, 1, 2, and 3, denote the lowest, middle,

and highest working frequency, respectively. There are two con-

siderations in designing a varactor-based antenna matching net-

work. First, the capacitance ratio between the maximum and

minimum capacitance which a varactor needs to provide must

fall within a reasonable range. Second, the topology of the

matching circuit should not be overly complex.

Figure 1 Impedance curve of the original antenna

Figure 2 Geometry of mender line antenna: (a) Antenna element (b)

Front view (c) Side view. [Color figure can be viewed in the online

issue, which is available at www.interscience.wiley.com] Figure 3 Diagram of matching circuit

DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 52, No. 8, August 2010 1787

For the impedance curve shown in Figure 1, a range of im-

pedance can be matched if the antenna is connected by a series

varactor, then followed by a shunt inductor. The shunt inductor

can move any impedance around the solid line circle area to the

matching point, where the origin of the Smith Chart is. The se-

ries varactor can move other impedance between markers 1 and

2 into the solid line circle. Through the combined effects of the

series varactor and shunt inductor, all impedance between

markers 1 and 2 can be matched.

Parametric studies and optimizations lead to the conclusion

that a meander line antenna element and a varactor with a ca-

pacitance ratio of 27.9 (25.1 pF/0.9 pF) are required to achieve

the 470–770 MHz bandwidth. To decrease the capacitance ratio

required by the varactor, a series inductor L1 is added to the

matching network. The final matching circuit layout is shown in

Figure 3.

For those impedances between markers 2 and 3 in Figure 1,

the antenna has reasonable return loss and its reactance varies

relative slowly when frequency changes. However, this segment

of impedance is beyond the reachable tuning range of a match-

ing circuit composed only of a series varactor and a shunt ca-

pacitor. With the addition of a series inductor, this segment of

the impedance line is moved from the bottom side to the upper

side of the solid line circle, and thus into the tunable range of

the matching circuit. Simulations indicate that the addition of

the extra series inductor reduces the required capacitance ratio

from 27.9 to 8.2 (7.7 pF/0.94 pF).

3. EXPERIMENT RESULTS

To verify the concept of the varactor tuning matching network,

a metallic meander line is selected as the antenna element. Spe-

cific dimensions are given in Figure 2 and its fabrication is

shown in Figure 4. The antenna element is made of a flat metal-

lic meander line. The element is folded and attached to the outer

side of a foam support, whose dimensions are 80 � 10 � 10

mm3. The antenna is installed on a single-sided FR4 board. The

size of the board is 140 � 80 mm2, with a thickness of 1.6 mm.

The impedance of the antenna without matching is shown in

Figure 1.

The proposed matching circuit is fabricated on a 10 � 10

mm2 double-sided FR4 board shown in Figure 5. Most of the

components labeled in Figure 5 correspond to Figure 3, with the

exceptions of Rb and Cp, which are a bias resistor and bypass

capacitor supplying bias voltage to the varactor. The varactor

used in the experiment is Skyworks SMV1247-079. The series

inductor L1 and shunt inductor L2 used in the experiment are

15 nH and 22 nH, respectively. The back of the matching cir-

cuit, a solid piece of copper and which also functions as the

ground, is soldered to the big board. Voltage is supplied by

three AA batteries. A variable resistor is used to adjust the bias

voltage.

Figure 6 shows measured return loss of the antenna with the

varactor bias voltage changes from 0 to 3.92 V. Clearly, it is

possible for operating frequency to be continuously tuned and

cover the whole DVB-H band with S11 better than �10 dB.

Based on the specification sheet, the capacitance values are 8.86

pF and 0.78 pF at 0 V and 3.92 V bias, respectively. This repre-

sents a capacitance ratio of 11.3 rather than the 8.2 obtained in

the simulation. It is believed that this discrepancy results from

the imperfection of the varactor and parasitic reactance from

lumped inductors and circuit board. Figure 7 shows the meas-

ured radiation patterns of proposed antenna at 520 and 720

Figure 6 Measured return loss

Figure 5 Layout of matching circuit

Figure 4 Fabrication of antenna. [Color figure can be viewed in the

online issue, which is available at www.interscience.wiley.com]

1788 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 52, No. 8, August 2010 DOI 10.1002/mop

MHz, a monopole-like pattern is achieved for vertical and hori-

zontal polarization.

4. CONCLUSIONS

A compact meander line monopole antenna with varactor-tuned

matching circuit for DVB-H application is proposed. The dimen-

sions of the prototype antenna are 80 � 10 � 10 mm3. The

antenna provides good coverage over the 470–770 MHz band-

width. The return loss over the entire bandwidth is better than

�10 dB.

ACKNOWLEDGMENTS

This work was supported by the National Basic Research Program

of China under Contract 2009CB320205, 2007CB310605, in part

by the National High Technology Research and Development Pro-

gram of China (863 Program) under Contract 2007AA01Z284, and

in part by the National Natural Science Foundation of China under

Contract 60771009.

REFERENCES

1. J. Holopainen, J. Villanen, M. Kyro, C. Icheln, and P. Vainikainen,

Antenna for handheld DVB terminal, Proceedings of the Interna-

tional Conference on Antenna Technology Small Antennas and

Novel Metamaterials, New York, USA, 2006, pp. 305–308.

2. M. Komulainen, M. Berg, H. Jantunen, and E. Salonen, Compact

varactor-tuned meander line monopole antenna for DVB-H signal

reception, Electron Lett 43 (2007), 1324–1326.

3. Z.D. Milosavljevic, A varactor tuned DVB-H antenna, Proceedings

of the International Conference on Antenna Technology Small

Antennas and Novel Metamaterials, Cambridge, UK, 2007, pp.

124–127.

VC 2010 Wiley Periodicals, Inc.

Figure 7 Measured radiation patterns: (a) y–z plane at 520 MHz (b) x–y plane at 520 MHz (c) y–z plane at 720 MHz (d) x–y plane at 720 MHz.

[Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com]

DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 52, No. 8, August 2010 1789